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Challenges of Meeting Dynamic Frequency Selection (DFS) Requirements

February 15, 2017

Dynamic Frequency Selection (DFS) requirements for products that operate in certain 5 GHz bands are now firmly established in most regions of the world. DFS is a mechanism that allows sharing of spectrum with radar systems operating in the 5250-5350 MHz, 5470-5725 MHz and in some regions of the world 5725-5850 MHz of the RF spectrum. Regulatory authorities required this sharing mechanism when the decision to open this spectrum up for uses like WiFi was adopted. The mechanism needed to verify that a channel is free of radar before using it, monitoring a channel for radar once a channel is in use, vacating the channel if radar is detected and remain off of a channel on which radar has been detected.

In some cases, the requirements have continued to evolve. For example, last year the FCC updated their testing procedures (KDB 905462 D02) for the Bin 5 radar type waveform to use a fixed width chirp in a given trial and changed which frequencies are used for each trial in the statistical performance check.

A continuing challenge is the requirement that the FCC pre test all products that are required to detect radar transmissions prior to a grant of equipment authorization being issued by a Certification Body. Depending on the FCC workload this can delay FCC certification by 1-3 months.

Since DFS compliance is primarily related to the software controlling a radio, it is necessary to involve software development personnel in DFS evaluation process that includes debug of issues found during testing. In addition, a description of how the product software that controls the radio DFS functions is secured to prevent tampering with by users of the product is necessary for product approval.

DFS testing involves different operation of the radio from other certification testing. Normal product operation with the added ability to restrict DFS functions and report detections are needed (KDB 905462 D04). Testing will proceed more quickly if a complete setup typical of actual use with the device configured to communicate with another product in a manner that produces a sufficiently high use of the channel (typically 17-30%). Additional information needed for performing the tests are the modes of operation, 99% bandwidth for each mode and antenna types and gains (testing with the lowest gain antennas is required).

If you have any questions regarding the best methods to ensure your DFS test session is successful to gain compliance, ask our experts or call 800-270-2516.